/Engine/Source/Runtime/GeometryCore/Public/Util/UniqueIndexSet.h
This is faster for construction than aTSet, but does require allocating and/or clearing the bit-array. Still generally quite a bit more efficient, particularly for large sets.
class FUniqueIndexSet
int64 *
Bits
int32
MaxIndex
int32
NumWords
TArray< int32 >
Values